Adenovirus E3-10.4K and 14.5K reduce surface levels of Fas and Inhibit Fas-mediated apoptosis in infected cells and recently, along with E3-6.7K, have been shown to have similar activities on TRAIL Receptors 1 and 2 (TR1 and TR2). 10.4K and 14.5K contain motifs relevant to protein trafficking. We propose to mutate these domains and assess the ability of the mutants to form complexes and to downregulate Fas, TR1 and TR2. Additionally, we will determine the requirement for these domains in inhibition of Fas- and TRAIL mediated apoptosis. Modulation of TR1 and TR2 is the first reported function for 6.7K. We proposed to study the interaction of 6.7K with 10.4K/14.5K and TR1 and TR2. 6.7K also contains a sorting motif which will be mutated, and the activity of the mutant 6.7K will be studied. Finally, we propose to identify other cellular proteins that interact with 6.7K by analyzing immunecomplexes containing 6.7 and by performing yeast two-hybrid screening using 6.7K as the bait. These experiments will elucidate how 6.7K modulates TR1 and TR2 and may identify other cellular factors that interact with this protein. The results of these experiments will clarify how 10.4K, 14.5K and 6.7K modulate death domain receptors and may identify novel activities for 6.7K. Moreover, they will increase our understanding of the mechanisms viruses use to evade immune regulation.